Orangutan Accounting 101

To save a species, scientists first need to know how many members it has left.

Credit: Photo: Eric Kilby/Flickr

The fruit of the rambutan tree is sour and sweet, like a grape. (It’s also red, furry and reminiscent of what I imagine snozzberries might look like.) The people of Indonesia love rambutan, and the tree is cultivated widely, both in commercial orchards and village gardens.

Orangutans also love rambutan. So when one of the great apes showed up in the canopy of the communal grove in a village near Lower Wajok, the locals tried to dislodge the primate with a dose of smoke. But then a gust of wind blew through the grove and everything went wrong.

The wind carried sparks up into the tree. The leaves ignited. And the orangutan’s coarse orange fur caught fire.

The primate died from his injuries several days later while the International Animal Rescue was transferring him to a treatment facility. His skin looked like the last hot dog left on a grill.

The tragedy of this tale doesn’t begin and end in that village grove. The underlying causes of why that orangutan was in the village for food in the first place come down to habitat loss, which is happening across the animal’s range, now limited only to rainforests on the islands of Borneo and Sumatra. Between 2000 and 2012 alone, Indonesia slashed and burned more than 23,000 square miles of primary forest. (That’s more than Brazil, one of the world’s most notorious deforesters, cleared during the same time period.)

According to Stephanie Spehar, a primatologist at the University of Wisconsin, Oshkosh, 75 percent of the orangutans on Borneo live outside of protected areas.

Rainforest destruction in West Kalimantan, Borneo.
Credit: Photo: David Gilbert, RAN/Flickr

When palm oil and acacia plantations destroy prime orangutan habitat, the animals that survive the razing often come into conflict with humans as they seek new territory or try to eke out a living among the plantations or within logging concessions. Unfortunately, Asia’s only great ape is not exactly welcome in those areas. Plantation owners see the animals as a threat to their cash crops, which orangutans like to eat. Some locals also still view the animals as a menu item, as evidenced by some graphic photos posted to Facebook earlier this year of a man proudly (albeit illegally) flame-broiling a whole orangutan.

The International Union for Conservation of Nature lists the Bornean orangutan as endangered. (The only other species of orangutan, the Sumatran, is critically endangered, with as few as 6,600 remaining on the island.) According to the most recent census on Borneo, taken in 2003, only 45,000 to 65,000 of these apes remain.

What’s worse is that Spehar says those numbers may be high, because here’s the thing—even though orangutans are big and orange and have a knack for attention-grabbing tree acrobatics, they are hard to count.

When researchers want to know how many are in an area, they start by counting nests, but it’s not an exact science. Orangutans are prolific nesters: Most can climb a tree, snap a few branches, and create a suitable bed in under five minutes, and most of these “man apes” won’t use a nest for more than one night. Mothers will sometimes, but not always, make multiple nests for their young. And nests also decay at different rates, depending on wind, sunlight, and moisture.

All these factors make deciphering whether one animal made all the nests in an area over a matter of days or weeks, or whether they are indicative of a group very challenging. And this subjective—and ultimately flawed—method for estimating orangutan populations has repercussions for conserving them.

“It’s extremely difficult to protect an endangered species if we don’t know how many are there,” says Brent Loken, executive director of Integrated Conservation and a PhD student at Simon Fraser University. Population statistics affect everything from IUCN statuses to protected area designations and conservation budgets.

Researchers examine a camera trap.
Credit: Photo: Brent Loken

In an effort to fix this problem, Spehar and Loken teamed up to look at how camera traps might be used to more accurately assess primate populations. (Their research will be published in the November issue of Biological Conservation, though it’s available online now.)

The team deployed 70 cameras in the Wehea Forest of East Kalimantan, Indonesia. After six months, they had 112 photos of orangutans, 67 of which were clear enough to identify individuals. The team looked for facial scars, hair color, nose and chin shapes, and other conspicuous characteristics to estimate how many orangutans inhabited the area.

A camera trap photo of an orangutan. Courtesy of Brent Loken.

They also performed a traditional nest count so they could compare results. The count indicated that there were 397 orangutans in the Wehea Forest. The camera traps? Just 60—around 15 percent of what the nest count projected. That’s a significant difference.

Both Spehar and Loken are quick to qualify the results as preliminary. For one, the cameras were initially positioned to capture the markings on the sides of clouded leopards. (This is the first time this type of photographic monitoring had ever been tried for these animals, so they didn’t know what would work best.) Next time, they hope to place more cameras at angles optimized for capturing the orangutans’ best side.

Despite the caveats, the scientists agree that with some fine-tuning, the camera-trap method may prove far more accurate than nest counts. But aside from better population estimates, there are other benefits to having a bunch of robot eyes in the bush.

“One of the cool things about camera traps is that you can actually identify and record poachers that come into the forest,” says Loken. He even approached several logging companies and showed them images of hunters caught on camera in an effort to call out the would-be poachers. (As you’d expect, no one fessed up.)

A camera trap photo of a clouded leopard. Courtesy of Brent Loken.

The cameras also provide scientists with a better picture of the health of the forest as a whole. The team’s traps captured images of 10 primate species in all, as well as clouded cats, a keystone species for the ecosystem.

Conservation efforts suffer from limited resources, and camera traps don’t come cheap. But knowing how many animals live in an area allows conservationists to prioritize what populations to target and to measure the impact of what strategies work best.

Conservation is often a numbers game. And if we’re going to save “the man of the forest,” we’re going to need better numbers.

This article was originally published on onEarth, which is no longer in publication. onEarth was founded in 1979 as the Amicus Journal, an independent magazine of thought and opinion on the environment. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. This article is available for online republication by news media outlets or nonprofits under these conditions: The writer(s) must be credited with a byline; you must note prominently that the article was originally published by NRDC.org and link to the original; the article cannot be edited (beyond simple things such grammar); you can’t resell the article in any form or grant republishing rights to other outlets; you can’t republish our material wholesale or automatically—you need to select articles individually; you can’t republish the photos or graphics on our site without specific permission; you should drop us a note to let us know when you’ve used one of our articles.

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